Using GNU Parallel with ia#

GNU Parallel is a shell tool for executing jobs in parallel. It is a very useful tool to use with ia for bulk jobs. It can be installed via many OS package managers.

For example, it can be installed via homebrew on Mac OS:

brew install parallel

Refer to the GNU Parallel homepage for more details on available packaes, source code, installation, and other documentation and tutorials.

Basic Usage#

You can use parallel to retrieve metadata from items concurrently:

$ cat itemlist.txt
$ cat itemlist.txt | parallel 'ia metadata {}' | jq

You can run parallel with --dry-run to check your commands before running them:

$ cat itemlist.txt | parallel --dry-run 'ia metadata {}'
ia metadata jj-test-2020-09-17-2
ia metadata jj-test-2020-09-17-1
ia metadata jj-test-2020-09-17-3

Logging and retrying with Parallel#

Parallel also offers an easy way to log and retry failed commands.

Here’s an example of a job that is retrieving metadata for all of the items in the file named itemlist.txt, and outputting the metadata to a file named output.jsonl. It uses the --joblog option to log all commands and their exit value to /tmp/my_ia_job.log:

$ cat itemlist.txt | parallel --joblog /tmp/my_ia_job.log 'ia metadata {}' > output.jsonl

You can now retry any commands that failed by using the --retry-failed option (don’t forget to switch > to >> in this example, so you don’t overwrite output.jsonl! >> means to append to the output file, rather than clobber it):

$ parallel --retry-failed --joblog /tmp/my_ia_job.log 'ia metadata {}' >> output.jsonl

If there were no failed commands, nothing will be rerun. You can rerun this command until it exits with 0. You can check the exit code by running echo $? directly after the parallel command finishes.